I have to admit, I've run into this problem too and find it quite annoying. I own 2 TIUs and remotes, I have the Wifi module and then as a complete separate system the DCS explorer. One example was I setup my monorail and because that's a semi portable layout, use the DCS explore rather than dragging around a TIU for one track- yet the DCS explorer will not control the monorail set and wants you to upgrade to using a TIU + wifi. And yes, also recently saw the same issue with an engine where the explorer was all but worthless and would not control it. This is purely one firmware update from working. Zero technical electronic reason- just they want you to spend more money. I really had high hopes for the DCS explorer and understood it has some limitations- but flat out not running a certain engine- that's just ridiculous. Again, Understand not supporting Premier features like quilling whistle, or other features, but not running an engine in the most basic mode just because of it's not in a list I support, is basically a breaking point.
And it's the price jump. A DCS explorer is what $135 or so street price? A TIU + Wifi is $315 -$350 street pricing. Again I don't mind a feature limitation (3 engines, no advanced features) but to not run a Proto 2 or 3 engine that isn't exactly special is just a really sore point with me too.
